Forming array contacts in semiconductor memories

ABSTRACT

Array contacts for semiconductor memories may be formed using a first set of parallel stripe masks and subsequently a second set of parallel stripe masks transverse to the first set. For example, one set of masks may be utilized to etch a dielectric layer, to form parallel spaced trenches. Then the trenches may be filled with a sacrificial material. That sacrificial material may then be masked transversely to its length and etched, for example. The resulting openings may be filled with a metal to form array contacts.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/066,340, filed on Oct. 29, 2013, which is as divisional of U.S.patent application Ser. No. 12/724,491 filed on Mar. 16, 2010, andissued as U.S. Pat. No. 8,569,891 on Oct. 29, 2013. These applicationsand patent are incorporated herein by reference, in their entirety, andfor any purpose.

BACKGROUND

This relates generally to semiconductor memories, such as non-volatilememories or volatile memories. Particularly, it relates to forming arraycontacts in memories.

Semiconductor memories may be volatile or non-volatile memories.Examples of volatile memories include dynamic random access memories(DRAMs) and static random access memories (SRAMs). Examples ofnon-volatile memories include Flash memories and resistive random accessmemories (ReRAM), such as phase change memories, to mention a fewexamples.

Typically, semiconductor memories include an array made up of parallelconductive rows and parallel conductive columns perpendicular to therows. Selectable memory cells are formed at the intersections of thoserows and columns.

Array contacts electrically connect elements in the array tometallization lines overlying the array. The array contacts then areconductive vias. With increasingly smaller memory cell sizes, arraycontacts need to effectively scale correspondingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, top plan view of one embodiment of the presentinvention at an early stage of manufacture;

FIG. 2 is a reduced cross-sectional view taken generally along the line2 2 in FIG. 1;

FIG. 3 is a cross sectional view corresponding to FIG. 2 at a subsequentstage in accordance with one embodiment;

FIG. 4 is a top plan view at a subsequent stage in accordance with theembodiment of FIGS. 1-3;

FIG. 5 is an enlarged, cross-sectional view taken generally along theline 5-5 in FIG. 4;

FIG. 6 is an enlarged, cross-sectional view of an alternate embodimentat a stage subsequent to the stage shown in FIG. 3 in accordance withone embodiment;

FIG. 7 is an enlarged, cross-sectional view at a subsequent stage tothat shown in FIG. 6 in accordance with one embodiment;

FIG. 8 is an enlarged top plan view of still another embodiment;

FIG. 9 is an enlarged top plan view at a subsequent stage; and

FIG. 10 is an enlarged top plan view at a subsequent stage.

DETAILED DESCRIPTION

In accordance with some embodiments, array contacts can be formedwithout some of the limitations typically imposed by conventionallithographic techniques. For example, conventional array contacts forhigh density arrays may be made using a dipole illumination mode forlithographic contact hole definition. One problem with this technique isthat the illumination mode results in an elliptical shape for thecontact where the X/Y ratio is reduced with reducing critical pitch.Overly elliptical contacts can sometimes result in integration issues interms of contact to gate distance.

In accordance with some embodiments of the present invention, at leastperpendicular masks and definition stages are used to define the arraycontacts instead of using the single mask, dipole illumination modetechnique. This may result, in some embodiments, in reducing theintegration issues that sometimes arise from an overly ellipticalcontact shape.

Referring to FIG. 1, a memory array 10 may include a plurality ofparallel, spaced conductive lines 16, extending generallyperpendicularly to parallel, spaced active areas 12, situated below thelines 16. The active areas are the regions where the memory cells areformed. The regions surrounding the lines 16 may be filled with adielectric 14, such as pre-metal deposition (PMD) oxide, over an etchstop layer (not shown) such as borderless nitride for example. However,other dielectrics may be used as well. The conductive lines 16 may, forexample, be control gates, in a Flash memory embodiment. However, thepresent invention is applicable to any semiconductor memory technology,including volatile and non-volatile memories.

A plurality of spaced parallel masks 18 may be aligned over theconductive lines 16, each mask 18 having dimensions slightly larger thanthe conductive lines 16. Thus, the masks 18 may extend in the samedirection as the conductive lines 16 and generally perpendicularly tothe active areas 12 in one embodiment. The masks 18 may be patternedphotoresist for example.

Referring to FIG. 2, the conductive lines 16 extend perpendicularlyacross the active areas 12. Other elements are not shown for simplicity.In this case 1 spaced, parallel tapered trenches 20 are formed betweenadjacent conductive lines 16. The trenches 20 extend in the samelengthwise direction and have the same pitch as the conductive lines 16in this embodiment. The trenches 20 may be formed using the masks 18,shown in FIG. 1 with dry etching for example. The mask 18 widths may bealtered by the etching process. The etching may stop on an etch stoplayer (not shown) at the bottom of the dielectric 14. In someembodiments, the etching is highly selective of the etch stop.

After etching, the masks 18 may be removed. In some embodiments, thetrenches 20 may taper inwardly from top to bottom as a result of theselected etching techniques. However, in other embodiments, verticalwall trenches may be formed.

Referring to FIG. 3, at this second masking stage, the trenches 20 maybe filled with trench filler 24 and planarized to the height of thedielectric 14. Examples of trench filler materials include nitrides,such as SiON, polysilicon, etc. Parallel spaced masks 22, formed of anysuitable material, including photoresist, may extend generallyperpendicularly to the lengths of the filled trenches 24. The masks 22may cover the region between the active areas 12, shown in FIG. 1. Thewidth of the masks 22 determines the desired spacing between resulting,later termed array contacts, as well as the thicknesses of those arraycontacts. A dry etching process used with masks 22 may be very selectiveto the selected trench filler 24, in some embodiments.

Moving to FIG. 4, the filled trenches 24 extend generally parallel tothe conductive lines 16 and may be situated between adjacent conductivelines. In the direction perpendicular to the trenches 24, the activeareas 12 extend parallel to one another. An array contact 26 may beformed in the active areas at the intersection between a trench filler24 and an active area 12. Other array contact pitches may so be used.

Thus, as shown in FIG. 5 1 the array contacts 26 are formed at thelocations never covered by the masks 18 or 22 (which have been removedat this point). The masks 18 and 22 are arranged perpendicularly to oneanother. An etchant may be used with the mask 22, which etchant ishighly selective of the pre-metal deposition oxide 14. As a result, onlythe trench filler 24 is removed. The masks 22 may then remove as well.

The resulting etched holes in the trench filler 24 may then filled bystandard barrier layers and metal, such as tungsten. Then, a standardchemical mechanical planarization process may be utilized to form thearray contacts 26, shown in FIG. 5. The array contacts 26 may becolumnar with a square or rectangular cross-section. The array contactsmay taper toward the semiconductor substrate. Thus, the contacts 26 maybe high aspect ratio or elongate, truncated pyramids. In some cases, theresulting array contacts 26 are more circular or elliptical because thecorners tend to etch away.

Referring to FIG. 6 1 in accordance with a dual damascene embodiment, inthe same region used to form the array contacts 26, the fill trenches 24are partially etched out, as indicated at 28. A dual damascene structurecan be formed in the same vertical space that was used to form the arraycontacts 26 in FIG. 5 in some embodiments. This may be important, insome embodiments, because the amount of vertical space may be limited.However, in some embodiments, the etch out step may not be used. Theetch out step entirely removes the upper portion of the trench filler24, extending into the page in FIG. 6, and leaving a verticallyshortened trench filler. A suitable wet etchant that selectively etchesthe trench filler 24 may be used in some embodiments.

Then, as shown FIG. 7, the remaining trench filler 24 may be removed atthe intersections of masks as described previously, resulting in thearray contacts 32. Where the upper layer of the trench filler 24 wasremoved, spaced parallel metal lines 30 may extend transversely to theconductive lines 16 and have array contacts 32 extend downwardly fromthe metal lines 30 between adjacent conductive lines 16. These metallines may, for example, be used as row or bit lines. The metal lines 30may be formed of the same or different materials.

Of course, the same process may be done in the reverse order wherein thestructure is first masked oil perpendicularly to the direction of theconductive lines 16 by forming masks 40 overlying the regions betweenadjacent active areas 12, as shown in FIG. 8. Dry etching may be used toform trenches 42 in the dielectric 14 between masks 40.

The intervening trenches 42 may be trench filled, for example, by asuitable material 44, as shown in FIG. 9. Then the trench fill material44 may be etched back to the height desired.

Thereafter the array contacts 46 may be formed by etching out the fillermaterial using masks 48 shown in FIG. 10. The contacts 46 are found atthe intersections of two masks, as shown in FIG. 10, by metal filling,followed by chemical mechanical planarization.

References throughout this specification to “one embodiment” or “anembodiment” mean that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneimplementation encompassed within the present invention. Thus,appearances of the phrase “one embodiment” or “in an embodiment” are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be instituted inother suitable forms other than the particular embodiment illustratedand all such forms may be encompassed within the claims of the presentapplication.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed:
 1. A method, comprising: filling parallel, spacedtrenches formed through a dielectric layer with a filler material;forming a plurality of masks extending perpendicularly to the length ofsaid filled trenches; etching the exposed portions of the filledtrenches to form openings in the filled trenches; and filling theopenings with a metal.
 2. The method of claim 1, further comprisingremoving the plurality of masks.
 3. The method of claim 1, furthercomprising: etching an upper portion of the metal; and etching an upperportion of the filled trenches.
 4. The method of claim 3, furthercomprising forming array contacts coupled to a metal line.
 5. The methodof claim 4, wherein the array contacts include the openings with themetal.
 6. The method of claim 4, further comprising forming the metalline and the array contacts in the same metallization.
 7. The method ofclaim 1, further comprising forming array contacts and metal lines in adual damascene process.
 8. The method of claim 1, further comprisingforming parallel spaced active areas and forming the trenches parallelto the active areas.
 9. The method of claim 8, wherein the parallelspaced active areas are formed below the trenches.
 10. The method ofclaim 1, further comprising forming parallel spaced active areas andforming said trenches perpendicular to the active areas.
 11. A methodcomprising: forming a plurality of parallel spaced filled trenches in adielectric material formed over a memory array; forming a plurality ofspaced openings along the length of each of the trenches of theplurality of parallel spaced filled trenches; and filling the pluralityof spaced openings with a metal to form array contacts.
 12. The methodof claim 11, further comprising forming a plurality of parallel spacedmasks extending transversely to the plurality of parallel spaced filledtrenches prior to forming a plurality of spaced openings along thelength of each of the trenches of the plurality of parallel spacedfilled trenches.
 13. The method of claim 11, further comprising etchingan upper portion of the plurality of parallel spaced filled trenches.14. The method of claim 13, further comprising forming metal lines inthe upper portion of the plurality of parallel spaced filled trenches.15. The method of claim 11, further comprising forming array contacts ofmetal lines in a dual damascene process.
 16. The method of claim 11,further comprising: forming parallel spaced active areas; and formingthe plurality of parallel spaced filled trenches perpendicular to theparallel spaced active areas.
 17. The method of claim 16, wherein theparallel spaced active areas are formed below the plurality of parallelspaced filled trenches.
 18. An apparatus, comprising: a memory array; adielectric material over said memory array; a filled trench in saiddielectric material; an opening along the length of the filled trench;and an array contact formed in the opening.
 19. The device of claim 18,wherein the dielectric material comprises a pre-metal deposition oxide.20. The device of claim 18, further comprising an etch stop layer overthe memory array below the dielectric material.
 21. The device of claim20, wherein the etch stop layer comprises a borderless nitride.